Method for filtering and cooling surface finishing compounds

ABSTRACT

Spent surface finishing compound is filtered and cooled or heated for reuse in a machine finishing process. The spent finishing compound is filtered through a pleated polyester or polypropylene wound filter cartridge to remove particles of a predetermined size ranging from about 0.5 to 100 microns. The surface finishing compound circulates through an in-line, constant flow intercooler having a chamber for receiving and maintaining the finishing compound in a spiral circulation. The surface finishing compound circulates about cooling tubes positioned within the chamber. Heat is exchanged between the circulating water within the cooling tubes and the surface finishing compound.

BACKGROUND OF THE INVENTION

In the surface finishing industry, machine tools are used to grind, cut,polish, lap, and finish the surfaces of plastic, metal, glass, andelectronic components. An example would be grinding and polishing ofplastic or glass optical lenses. These finishing processes utilizeabrasives, polishing compounds, and coolants, all generally referred toas surface finishing compounds or slurries. The coolants generally areformulated with lubricants, rust inhibitors, and other surface activeagents for cleanliness and low-foaming characteristics.

During the machine finishing processes, the surface finishing compoundsbecome contaminated with impurities which may include plastic, glass,and ceramic particles, abrasive grains and binding agents, and otherferrous and nonferrous particles. The surface finishing compoundsfurther are heated as a result of the friction generated during themachining processes.

It is economically desirable to recycle and reuse the surface finishingcompounds which have been spent in the machine finishing process. Thisgenerally requires that the impurities be removed and the resultingsurface finishing compounds be chilled to the desired coolingtemperature. In certain unique circumstances, such as the use of rareearth oxide polishing compounds, it may be necessary to heat thefinishing compounds to a desired temperature for best results.

The present filtering and cooling/heating systems for finishingcompounds use a wide variety of options. Filtering is accomplished,among other methods, by: settling tanks; paper, fabric or cartridgemedia; hydrocyclones; or centrifuges. The finishing compounds andslurries generally are chilled or heated through a system of pumps andtanks or reservoirs. The surface finishing compound or slurry is storedtemporarily in a storage tank or reservoir which has been fitted withrefrigerant coils connected to a typical chiller. The chiller and coilschill the finishing compound to the desired temperature before it isreused in the process. When heating is desired, heater coils are used inlieu of refrigerant coils.

The problem, which is one of the bases for the invention, is that thepresent filtering and cooling/heating systems use a maze of filters,pumps and tanks to prepare the recycled surface finishing compounds.These systems are expensive to install, operate and maintain and take upextensive floor space at the site of the finishing processes.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an improved method forfiltering and cooling/heating surface finishing compounds and otherslurries.

Another object of the present invention is to provide a new and improvedprocess and apparatus for cooling or heating surface finishingcompounds.

A further object of the present invention is to reduce the capital andoperating expenses and reduce the floor space requirements for afiltering and cooling/heating system for surface finishing compounds andother slurries.

Another object of the present invention is to provide an improved methodfor filtering and cooling/heating hazardous surface finishing compounds.

Further objects and improvements of the present invention will beapparent upon reading the specification and claims.

According to the present invention, spent surface finishing compound iscollected from a machine finishing process. The spent compound isfiltered through a pleated polyester or polypropylene wound filtercartridge to remove particles of a predetermined size ranging from about0.1 to 100 microns and larger.

The surface finishing compound then is transferred through an in-line,constant flow intercooler having a chamber for receiving and maintainingthe finishing compound in a spiral circulation. The surface finishingcompound circulates about cooling tubes positioned within the chamber tocool the finishing compound. The cooling tubes carry cooling fluidcirculated from a chiller unit. The recycled surface finishing compoundis returned to the machine finishing process. Depending on the use andtype of finishing compound, the in-line intercooler may be used to heatthe finishing compound in lieu of cooling the compound.

The intercooler includes a cylindrical chamber and continuous coolingtubes looping in a generally parallel, spaced relationship along theaxis of the cylindrical chamber. The surface finishing compound entersthe chamber at one end of cylindrical chamber in a direction generallytangent to the wall of the cylindrical chamber and perpendicular to theaxis of the cylindrical chamber. This arrangement causes the finishingcompound to swirl or spiral about the cooling tubes, which are spacedfrom the inner wall of the cylindrical chamber, until the finishingcompound exits at the opposite end of the cylindrical chamber.

These and other objects, advantages, and features of the invention willbe set forth in the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of the method for filtering andcooling surface finishing compounds according to the present invention;

FIG. 2 is a perspective and cross-sectional representation of thein-line intercooler according to the present invention; and

FIG. 3 is a section 3--3 through the intercooler according to FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Surface finishing compounds include, but are not limited to, abrasives,polishing compounds, and coolants used in connection with the grinding,cutting, lapping, polishing, finishing, or other machining of glass,metal, plastic, electronic component or similar surfaces. Examples ofsurface finishing compounds include, but are not limited to, ceralumalumina, silicon carbide, boron carbide, aluminum oxide, corundumpowder, synthetic and water coolants, silica, quartz, aluminum, silicon,cerium oxide, rare earth oxides, and zirconium oxide.

FIG. 1 depicts a system 8 for filtering and cooling a surface finishingcompound which has been spent in connection with a machine finishingprocess. The spent surface finishing compound is recycled for reuse inthe machine finishing process. Depending on the nature of the finishingcompound and machine finishing process, the system may be implemented toheat the finishing compound instead of cooling the compound.

Referring to FIG. 1, the spent surface finishing compound is collectedfrom the machine finishing process (not shown). The finishing compoundis pumped or delivered to the intake manifold 12 at inlet 10. A pressuregauge 16 and an adjustable diaphragm pressure sensor 14 are connected tothe intake manifold 12, which provides a means for gaugeinstrumentation.

The pressure sensor 14 detects the fluid pressure in the intake manifold12 and compares it to preset pressure points ranging from about 0 to 60psi. When the fluid pressure in the intake manifold 12 reaches a presetlevel, for example at 22 psi, the pressure sensor 14 activates thesolenoid valve 52 and may activate a typical alarm or warning light (notshown). The solenoid valve 52 opens to permit the finishing compound tobypass the discharge manifold 42 through bypass return line 54 for thereasons explained below. The pressure sensor 14 monitors a rise in fluidpressure which may indicate the need to change the filters 28 and 30 orthat the flow of the finishing compound to the machine finishing processhas been shut off or blocked. In this fashion, the pressure sensor 14serves as a safety mechanism.

The spent finishing compound flows from the intake manifold 12 to thefilters 28 and 30. Isolation and shutoff valves 20, 22, 24, and 26permit the filters 28 and 30 to be used on line separately or incombination. Any number of filters may be used. In addition, a bypassline (not shown) could be used to bypass the filters when the fluidpressure in the intake manifold 12 reaches a preset level or when thefilters are cleaned or changed.

The filters preferably are standard pleated polyester cartridge type orpolypropylene fiber wound cartridge type. These filters are availablecommercially. An example would be the Excel models manufactured by EdenEquipment Company. The nominal pore sizes generally range between about0.1 and 100 microns. A typical pleated filter would have four squarefeet of media per ten inches of filter cartridge length. The filters 28and 30 are adapted to remove substantially the impurities and particlesin the finishing compounds having a size greater than the nominal poresize of the filters. Alternative filtering methods such ashydrocyclones, centrifuges, and the like could be used.

The filtered finishing compound flows from the filters 28 and 30 throughfeed line 32 to the intercooler 34. The intercooler 34 has a chamber forreceiving and maintaining the finishing compound in a spiralcirculation. Referring to FIGS. 2 and 3, the intercooler 34 includes acylindrical chamber 56, intercooler inlet 58, intercooler outlet 60, andcooling tubes 55. The cylindrical chamber 56 has a cylindrical sidewall61, top portion 57, and bottom portion 59. The cylindrical chamber maybe Schedule 40 PVC, stainless steel or similar materials.

The cooling tubes 55 are looped continuously in a generally parallel,spaced relationship along the axis 72 of the cylindrical chamber 56. Thecooling tubes 55 include multiple legs 66 and loops 68 and 70 which arearranged in a spaced relationship from the chamber sidewall 61. Apreferred arrangement has ten or twelve legs and loops. The materials ofthe cooling tubes could be copper or stainless steel.

The circulating water or fluid enters the cooling tubes 55 throughcirculating water inlet 38 which penetrates the closed chamber topportion 57. The circulating water exits the cooling tubes 55 throughcirculating water outlet 36 which penetrates the closed chamber bottomportion 59. The direction of the flow of the circulating water or fluidcould be reversed.

The circulating water is cooled or heated, depending on the desiredtemperature change for the finishing compounds, and then circulatedthrough a typical arrangement of water circulation pumps, valving,piping and temperature control units. The temperature control units canbe standard chiller units for cooling or standard heating units forheating the circulating water. The intercooler and its in-line, constantflow cooling/heating features eliminate the need for conventional,inefficient storage tanks having cooling/heating coils to cool or heatthe entire contents. As a result, the temperature control units can bedownsized from the units used in conventional processes. Typical chillerunits include the Temprite TR Series.

The surface finishing compound 64 enters the cylindrical chamber 56through intercooler inlet 58 in a direction generally tangent to thesidewall 61 and perpendicular to the axis 72 of the cylindrical chamber.This arrangement causes the finishing compound to swirl or spiral aboutthe cooling tubes until the finishing compound exits 62 at the oppositeend through intercooler outlet 60. Heat is exchanged between thecirculating water and the finishing compound to bring the finishingcompound to the desired temperature. The intercooler inlet and outletcan be positioned at various other locations. An alternative arrangementwould permit the circulating water to flow through the cylindricalchamber and the finishing compound to flow through the cooling tubes.

The finishing compound is delivered from the intercooler 34 throughmanifold inlet 40 to the discharge manifold 42. Temperature probes 44and 46 and solenoid valve 52 are connected to the discharge manifold 42.The temperature probe 42 can be the capillary tube type which controls athermostat. The thermostat is electrically connected to the controls ofthe water circulating pump for determining the flow rate of thecirculating water or fluid having a present temperature. The circulatingwater flow rate, in turn, controls the amount of heat exchanged in theintercooler. Alternatively, the temperature of the circulating water maybe changed to control the amount of heat exchanged. Temperature probe 44also can be the capillary tube type and provides a temperature gauge tomonitor visually the temperature of the finishing compound leaving theintercooler. Other types of temperature probes could be used.

The solenoid valve 52 is electrically connected to the pressure sensor14. The solenoid valve 52 opens when the pressure detected in the intakemanifold 12 exceeds a preset level. In these circumstances, the finishedcompound would partially or entirely bypass the discharge line 48 of thedischarge manifold 42 and pass through the bypass return 54. Thebypassed finishing compound would be returned to the inlet 10 or astorage basin and would not be returned directly to the machinefinishing process. The recycled finishing compound leaves the dischargeline 48 and is delivered for reuse in the surface machine finishingprocess.

The entire system 8 is arranged in a compact fashion and mounted on acabinet with casters. The monitoring controls can be mounted on a panel.

The present invention was tested with satisfactory filtering and coolingof finishing compounds used in connection with four machines polishingCR-39 plastic optical lenses and two machines polishing polycarbonateoptical lenses. The finishing compound was alumina-based polishingslurry at 2 micron average particle size. Tests were run with two20-inch pleated polyester cartridge type filters and two 20-inchpolypropylene fiber wound cartridge type filters. The cooling water wassupplied at a rate of approximately 9.6 gph at an average temperature of60° F. from a Temprite TR-10 chiller. The polishing compound wasrecycled at a rate of approximately 19 gpm and maintained at an ambienttemperature of 70° F. The intercooler was four inches in diameter andapproximately 24 inches in length. The cooler tubes were 1/2-inch size.The average starting pressure was 18 psi, and the filters were changedwhen the pressure increased to approximately 22 psi.

Under the described conditions, the filter life and number of lenssurfaces polished during that period were as follows:

    ______________________________________                                                                Average                                                             Average Filter                                                                          Number of                                                           Life, hours                                                                             Surfaces Polished                                     ______________________________________                                        Pleated Polyester Filter                                                      30 Micron Pore  16          457                                               Polypropylene Fiber Filter                                                    50 Micron Pore  40          1,643                                             30 Micron Pore  24          975                                               ______________________________________                                    

Since the invention, as disclosed herein, may be embodied in otherspecific forms without departing from its spirit or centralcharacteristics, the preferred embodiment described herein is thereforeto be considered in all respects as illustrative and not restrictive.The scope of the invention is indicated by the following claims ratherthan the foregoing description, and all changes that come within themeaning and range of equivalency of the claims are therefore intended tobe embraced in the claims.

What is claimed is:
 1. A method for recycling spent finishing compoundsused in surface machine finishing processes, comprising the steps of:a.collecting the spent finishing compound used in a surface machinefinishing process; b. filtering the spent finishing compound to removeparticles of a predetermined size ranging from about 0.1 to 100 microns;c. transferring the spent finishing compound through an in-line,constant flow intercooler having a chamber for receiving and maintainingthe finishing compound in a spiral circulation and having cooling tubes;d. circulating fluid having a preset temperature from a temperaturecontrol unit to the cooling tubes of the intercooler about which thefinishing compound circulates to change the temperature of the finishingcompound to a predetermined level; and e. returning the finishingcompound to the surface machine finishing process.
 2. The methodaccording to claim 1 wherein the temperature control unit is a chillerunit for controlling the temperature of the circulating fluid todecrease the temperature of the finishing compound to a predeterminedlevel.
 3. The method according to claim 2 which includes the step ofmonitoring the temperature of the finishing compound leaving theintercooler and adjusting the flow rate of the circulating fluid tochange the rate of cooling in response to a deviation from apredetermined temperature of the finishing compound.
 4. The methodaccording to claim 1 which includes the step of monitoring the pressurelevel of the finishing compound and diverting the recycled finishingcompound from returning to the surface machine finishing process when apredetermined pressure is exceeded.
 5. The method according to claimwherein the spent finishing compound is filtered to remove particles ofa predetermined size ranging from about 20 to 50 microns.
 6. The methodaccording to claim 1 wherein the intercooler includes a cylindricalchamber having an axis, a cylindrical chamber sidewall, an intercoolerinlet, and an intercooler outlet, the cooling tubes having a circulatingfluid inlet, a circulating fluid outlet, and multiple legs and loopswhich are connected and looped continuously in a substantially parallel,spaced relationship along the axis of the cylindrical chamber, thecooling tubes further arranged in a spaced relationship from the chambersidewall.
 7. The method according to claim 6 wherein the cooling tubeshave at least ten legs and ten loops.
 8. The method according to claim 6wherein the intercooler inlet is positioned in a direction substantiallytangent to the chamber sidewall and substantially perpendicular to theaxis of the cylindrical chamber.
 9. The method according to claim 6wherein the cylindrical chamber further includes a closed first endportion and closed second portion, the circulating fluid inletpenetrates the first end portion and the circulating fluid outletpenetrates the second end portion permitting the circulating fluid toflow to and from the cooling tubes positioned within the cylindricalchamber.